From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <gcc-bugzilla@gcc.gnu.org>
Received: by sourceware.org (Postfix, from userid 48)
 id AB8763858430; Tue, 15 Feb 2022 18:10:22 +0000 (GMT)
DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org AB8763858430
From: "cvs-commit at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/100874] [12 Regression] slight missed optimization with
 min<a,CST>-CST on aarch64 (subs_compare_2.c)
Date: Tue, 15 Feb 2022 18:10:22 +0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: changed
X-Bugzilla-Watch-Reason: None
X-Bugzilla-Product: gcc
X-Bugzilla-Component: target
X-Bugzilla-Version: 12.0
X-Bugzilla-Keywords: missed-optimization, testsuite-fail
X-Bugzilla-Severity: normal
X-Bugzilla-Who: cvs-commit at gcc dot gnu.org
X-Bugzilla-Status: UNCONFIRMED
X-Bugzilla-Resolution: 
X-Bugzilla-Priority: P3
X-Bugzilla-Assigned-To: unassigned at gcc dot gnu.org
X-Bugzilla-Target-Milestone: 12.0
X-Bugzilla-Flags: 
X-Bugzilla-Changed-Fields: 
Message-ID: <bug-100874-4-k0AIdtw5kv@http.gcc.gnu.org/bugzilla/>
In-Reply-To: <bug-100874-4@http.gcc.gnu.org/bugzilla/>
References: <bug-100874-4@http.gcc.gnu.org/bugzilla/>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
X-Bugzilla-URL: http://gcc.gnu.org/bugzilla/
Auto-Submitted: auto-generated
MIME-Version: 1.0
X-BeenThere: gcc-bugs@gcc.gnu.org
X-Mailman-Version: 2.1.29
Precedence: list
List-Id: Gcc-bugs mailing list <gcc-bugs.gcc.gnu.org>
List-Unsubscribe: <https://gcc.gnu.org/mailman/options/gcc-bugs>,
 <mailto:gcc-bugs-request@gcc.gnu.org?subject=unsubscribe>
List-Archive: <https://gcc.gnu.org/pipermail/gcc-bugs/>
List-Post: <mailto:gcc-bugs@gcc.gnu.org>
List-Help: <mailto:gcc-bugs-request@gcc.gnu.org?subject=help>
List-Subscribe: <https://gcc.gnu.org/mailman/listinfo/gcc-bugs>,
 <mailto:gcc-bugs-request@gcc.gnu.org?subject=subscribe>
X-List-Received-Date: Tue, 15 Feb 2022 18:10:22 -0000

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D100874

--- Comment #4 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The trunk branch has been updated by Richard Sandiford <rsandifo@gcc.gnu.or=
g>:

https://gcc.gnu.org/g:8e84b2b37a541b27feea69769fc314d534464ebd

commit r12-7249-g8e84b2b37a541b27feea69769fc314d534464ebd
Author: Richard Sandiford <richard.sandiford@arm.com>
Date:   Tue Feb 15 18:09:35 2022 +0000

    aarch64: Fix subs_compare_2.c regression [PR100874]

    subs_compare_2.c tests that we can use a SUBS+CSEL sequence for:

    unsigned int
    foo (unsigned int a, unsigned int b)
    {
      unsigned int x =3D a - 4;
      if (a < 4)
        return x;
      else
        return 0;
    }

    As Andrew notes in the PR, this is effectively MIN (x, 4) - 4,
    and it is now recognised as such by phiopt.  Previously it was
    if-converted in RTL instead.

    I tried to look for ways to generalise this to other situations
    and to other ?:-style operations, not just max and min.  However,
    for general ?: we tend to push an outer =C3=A2- CST=C3=A2 into the arms=
 of
    the ?: -- at least if one of them simplifies -- so I didn't find
    any useful abstraction.

    This patch therefore adds a pattern specifically for
    max/min(a,cst)-cst.  I'm not thrilled at having to do this,
    but it seems like the least worst fix in the circumstances.
    Also, max(a,cst)-cst for unsigned a is a useful saturating
    subtraction idiom and so is arguably worth its own code
    for that reason.

    gcc/
            PR target/100874
            * config/aarch64/aarch64-protos.h (aarch64_maxmin_plus_const):
            Declare.
            * config/aarch64/aarch64.cc (aarch64_maxmin_plus_const): New
function.
            * config/aarch64/aarch64.md (*aarch64_minmax_plus): New pattern.

    gcc/testsuite/
            * gcc.target/aarch64/max_plus_1.c: New test.
            * gcc.target/aarch64/max_plus_2.c: Likewise.
            * gcc.target/aarch64/max_plus_3.c: Likewise.
            * gcc.target/aarch64/max_plus_4.c: Likewise.
            * gcc.target/aarch64/max_plus_5.c: Likewise.
            * gcc.target/aarch64/max_plus_6.c: Likewise.
            * gcc.target/aarch64/max_plus_7.c: Likewise.
            * gcc.target/aarch64/min_plus_1.c: Likewise.
            * gcc.target/aarch64/min_plus_2.c: Likewise.
            * gcc.target/aarch64/min_plus_3.c: Likewise.
            * gcc.target/aarch64/min_plus_4.c: Likewise.
            * gcc.target/aarch64/min_plus_5.c: Likewise.
            * gcc.target/aarch64/min_plus_6.c: Likewise.
            * gcc.target/aarch64/min_plus_7.c: Likewise.=